Preliminary evidence for human globus pallidus pars interna neurons signaling reward and sensory stimuli

Managing impulse control and related behavioral disorders in Parkinson's disease: where we are in 2025?

INTRODUCTION

Impulse control and related behavioral disorders (ICBDs) commonly complicate Parkinson's disease (PD) course. The ICBDs spectrum encompasses two groups of conditions, with distinct pathophysiology: proper 'impulse control disorders (ICDs)' (e.g. gambling) and the 'ICDs related disorders (ICDs-RD)' (e.g. punding). Behavioral disturbances are associated with dopamine replacement therapies. ICBDs affect quality of life of patients and caregivers, making their management essential for reducing PD overall burden.

AREAS COVERED

This article reviews current management strategies for ICBDs in PD. The authors highlight strengths and limitations of these strategies, and explore the potential role of emerging treatment options, giving particular focus to new compounds and invasive therapies.

EXPERT OPINION

Prevention, close monitoring, and caregiver involvement are essential in managing ICBDs in PD. Treatment approaches should be tailored to ICBDs' functional impact and aimed to reduce the pulsatile stimulation of dopamine receptors, especially D2. Dopamine agonist (DA) tapering remains the primary therapeutic approach, alongside psychotherapy and second-line agents, like atypical antipsychotics and serotonin-noradrenaline reuptake inhibitors. Insights into ICDs pathophysiology and DA-specific pharmacodynamics indicate safer profiles for certain preparations (e.g. rotigotine patches) and possibly for D1/D5 agonists like tavapadon. Invasive treatments, including deep brain stimulation and infusion therapies, should be prioritized in advanced-stage PD complicated by ICBDs.

Invasive neurophysiological recordings in human basal ganglia. What have we learned about non-motor behaviour?

Research into the function of deep brain structures has benefited greatly from microelectrode recordings in animals. This has helped to unravel physiological processes in the healthy and malfunctioning brain. Translation to the human is necessary for improving basic understanding of subcortical structures and their implications in diseases. The use of microelectrode recordings as a standard component of deep brain stimulation surgery offers the most viable route for studying the electrophysiology of single cells and local neuronal populations in important deep structures of the human brain. Most of the studies in the basal ganglia have targeted the motor loop and movement disorder pathophysiology. In recent years, however, research has diversified to include limbic and cognitive processes. This review aims to provide an overview of advances in neuroscience made using intraoperative and post-operative recordings with a focus on non-motor activity in the basal ganglia.

Model of a striatal circuit exploring biological mechanisms underlying decision-making during normal and disordered states

Decision-making requires continuous adaptation to internal and external contexts. Changes in decision-making are reliable transdiagnostic symptoms of neuropsychiatric disorders. We created a computational model demonstrating how the striosome compartment of the striatum constructs a mathematical space for decision-making computations depending on context, and how the matrix compartment defines action value depending on the space. The model explains multiple experimental results and unifies other theories like reward prediction error, roles of the direct versus indirect pathways, and roles of the striosome versus matrix, under one framework. We also found, through new analyses, that striosome and matrix neurons increase their synchrony during difficult tasks, caused by a necessary increase in dimensionality of the space. The model makes testable predictions about individual differences in disorder susceptibility, decision-making symptoms shared among neuropsychiatric disorders, and differences in neuropsychiatric disorder symptom presentation. The model reframes the role of the striosomal circuit in neuroeconomic and disorder-affected decision-making.

Highlights

Striosomes prioritize decision-related data used by matrix to set action values. Striosomes and matrix have different roles in the direct and indirect pathways. Abnormal information organization/valuation alters disorder presentation. Variance in data prioritization may explain individual differences in disorders.

eTOC

Beck et al. developed a computational model of how a striatal circuit functions during decision-making. The model unifies and extends theories about the direct versus indirect pathways. It further suggests how aberrant circuit function underlies decision-making phenomena observed in neuropsychiatric disorders.

Topological differences of striato-thalamo-cortical circuit in functional brain network between premature ejaculation patients with and without depression

INTRODUCTION

Premature ejaculation (PE), a common male sexual dysfunction, often accompanies by abnormal psychological factors, such as depression. Recent neuroimaging studies have revealed structural and functional brain abnormalities in PE patients. However, there is limited neurological evidence supporting the comorbidity of PE and depression. This study aimed to explore the topological changes of the functional brain networks of PE patients with depression.

METHODS

Resting-state functional magnetic resonance imaging (rs-fMRI) data were acquired from 60 PE patients (30 with depression and 30 without depression) and 29 healthy controls (HCs). Functional brain networks were constructed for all participants based on rs-fMRI data. The nodal parameters including nodal centrality and efficiency were calculated by the method of graph theory analysis and then compared between groups. In addition, the results were corrected for multiple comparisons by family-wise error (FWE) (p < .05).

RESULTS

PE patients with depression had increased degree centrality and global efficiency in the right pallidum, as well as increased degree centrality in the right thalamus when compared with HCs. PE patients without depression showed increased degree centrality in the right pallidum and thalamus, as well as increased global efficiency in the right precuneus, pallidum, and thalamus when compared with HCs. PE patients with depression demonstrated decreased degree centrality in the right pallidum and thalamus, as well as decreased global efficiency in the right precuneus, pallidum, and thalamus when compared to those without depression. All the brain regions above survived the FWE correction.

CONCLUSION

The results suggested that increased and decreased functional connectivity, as well as the capability of global integration of information in the brain, might be related to the occurrence of PE and the comorbidity depression in PE patients, respectively. These findings provided new insights into the understanding of the pathological mechanisms underlying PE and those with depression.

The Functional Neuroimaging of Autobiographical Memory for Happy Events: A Coordinate-Based Meta-Analysis

Neuroimaging studies using autobiographical recall methods investigated the neural correlates of happy autobiographical memories (AMs). The scope of the present activation likelihood estimation (ALE) meta-analysis was to quantitatively analyze neuroimaging studies of happy AMs conducted with autobiographical recall paradigms. A total of 17 studies (12 fMRI; 5 PET) on healthy individuals were included in this meta-analysis. During recall of happy life events, consistent activation foci were found in the frontal gyrus, the cingulate cortex, the basal ganglia, the parahippocampus/hippocampus, the hypothalamus, and the thalamus. The result of this quantitative coordinate-based ALE meta-analysis provides an objective view of brain responses associated with AM recollection of happy events, thus identifying brain areas consistently activated across studies. This extended brain network included frontal and limbic regions involved in remembering emotionally relevant positive events. The frontal gyrus and the cingulate cortex may be responsible for cognitive appraisal processes during recollection of happy AMs, while the subthalamic nucleus and globus pallidus may be involved in pleasure reactions associated with recollection of happy life events. These findings shed light on the neural network involved in recalling positive AMs in healthy individuals, opening further avenues for future research in clinical populations with mood disorders.

Uncovering the neurophysiology of mood, motivation and behavioral symptoms in Parkinson's disease through intracranial recordings

Neuropsychiatric mood and motivation symptoms (depression, anxiety, apathy, impulse control disorders) in Parkinson's disease (PD) are highly disabling, difficult to treat and exacerbated by current medications and deep brain stimulation therapies. High-resolution intracranial recording techniques have the potential to undercover the network dysfunction and cognitive processes that drive these symptoms, towards a principled re-tuning of circuits. We highlight intracranial recording as a valuable tool for mapping and desegregating neural networks and their contribution to mood, motivation and behavioral symptoms, via the ability to dissect multiplexed overlapping spatial and temporal neural components. This technique can be powerfully combined with behavioral paradigms and emerging computational techniques to model underlying latent behavioral states. We review the literature of intracranial recording studies investigating mood, motivation and behavioral symptomatology with reference to 1) emotional processing, 2) executive control 3) subjective valuation (reward & cost evaluation) 4) motor control and 5) learning and updating. This reveals associations between different frequency specific network activities and underlying cognitive processes of reward decision making and action control. If validated, these signals represent potential computational biomarkers of motivational and behavioural states and could lead to principled therapy development for mood, motivation and behavioral symptoms in PD.

Distinct Roles of the Human Subthalamic Nucleus and Dorsal Pallidum in Parkinson's Disease Impulsivity

BACKGROUND

Impulsivity and impulse control disorders are common in Parkinson's disease and lead to increased morbidity and reduced quality of life. Impulsivity is thought to arise from aberrant reward processing and inhibitory control, but it is unclear why deep brain stimulation of either the subthalamic nucleus (STN) or globus pallidus internus (GPi) affects levels of impulsivity. Our aim was to assess the role of the STN and GPi in impulsivity using invasive local field potential (LFP) recordings from deep brain stimulation electrodes.

METHODS

We measured LFPs during a simple rewarding Go/NoGo paradigm in 39 female and male human patients with Parkinson's disease manifesting variable amounts of impulsivity who were undergoing unilateral deep brain stimulation of either the STN (18 nuclei) or GPi (28 nuclei). We identified reward-specific LFP event-related potentials and correlated them to impulsivity severity.

RESULTS

LFPs in both structures modulated during reward-specific Go and NoGo stimulus evaluation, reward feedback, and loss feedback. Motor and limbic functions were anatomically separable in the GPi but not in the STN. Across participants, LFP reward processing responses in the STN and GPi uniquely depended on the severity of impulsivity.

CONCLUSIONS

This study establishes LFP correlates of impulsivity within the STN and GPi regions. We propose a model for basal ganglia reward processing that includes the bottom-up role of the GPi in reward salience and the top-down role of the STN in cognitive control.

Cognitive task-related oscillations in human internal globus pallidus and subthalamic nucleus

Recently it has been acknowledged that the basal ganglia nuclei play a major role in cognitive control; however, the contribution by their network remains unclear. Previous studies have demonstrated the role of the subthalamic nucleus (STN) in cognitive processing and suggested that its connections to cortical and other associated regions regulate response inhibition during conflict conditions. By contrast, the role of the internal globus pallidus (GPi) as the output nucleus before the thalamic relay has not yet been investigated during cognitive processing. We recorded local field potentials (LFPs) from externalized deep brain stimulation (DBS) electrodes implanted bilaterally in the GPi (n=9 participants with dystonia) and STN (n=8 participants with Parkinson's disease (PD)) during a primed flanker task. Both dystonia (GPi group) and PD participants (STN group) responded faster to the congruent trials than the incongruent trials. Overall, the dystonic GPi group was significantly faster than the PD STN group. LFPs showed elevated cue-triggered theta (3-7Hz) power in GPi and STN groups in a similar way. Response-triggered LFP beta power (13-25Hz) was significantly increased in the GPi group compared to the STN group. Results demonstrate that GPi activity appears to be critical in the cognitive processing of action selection and response during the presence of conflict tasks similar to the STN group.

Long-Known Music Exposure Effects on Brain Imaging and Cognition in Early-Stage Cognitive Decline: A Pilot Study

BACKGROUND

Repeated exposure to long-known music has been shown to have a beneficial effect on cognitive performance in patients with AD. However, the brain mechanisms underlying improvement in cognitive performance are not yet clear.

OBJECTIVE

In this pilot study we propose to examine the effect of repeated long-known music exposure on imaging indices and corresponding changes in cognitive function in patients with early-stage cognitive decline.

METHODS

Participants with early-stage cognitive decline were assigned to three weeks of daily long-known music listening, lasting one hour in duration. A cognitive battery was administered, and brain activity was measured before and after intervention. Paired-measures tests evaluated the longitudinal changes in brain structure, function, and cognition associated with the intervention.

RESULTS

Fourteen participants completed the music-based intervention, including 6 musicians and 8 non-musicians. Post-baseline there was a reduction in brain activity in key nodes of a music-related network, including the bilateral basal ganglia and right inferior frontal gyrus, and declines in fronto-temporal functional connectivity and radial diffusivity of dorsal white matter. Musician status also significantly modified longitudinal changes in functional and structural brain measures. There was also a significant improvement in the memory subdomain of the Montreal Cognitive Assessment.

CONCLUSION

These preliminary results suggest that neuroplastic mechanisms may mediate improvements in cognitive functioning associated with exposure to long-known music listening and that these mechanisms may be different in musicians compared to non-musicians.

Deep brain stimulation for the treatment of cerebral palsy: A review

Deep brain stimulation (DBS) has been used as a safe and effective neuromodulation technique for treatment of various diseases. A large number of patients suffering from movement disorders such as dyskinesia may benefit from DBS. Cerebral palsy (CP) is a group of permanent disorders mainly involving motor impairment, and medical interventions are usually unsatisfactory or temporarily active, especially for dyskinetic CP. DBS may be another approach to the treatment of CP. In this review we discuss the targets for DBS and the mechanisms of action for the treatment of CP, and focus on presurgical assessment, efficacy for dystonia and other symptoms, safety, and risks.

Hemispheric Asymmetry of Globus Pallidus Relates to Alpha Modulation in Reward-Related Attentional Tasks

Whereas subcortical structures such as the basal ganglia have been widely explored in relation to motor control, recent evidence suggests that their mechanisms extend to the domain of attentional switching. We here investigated the subcortical involvement in reward related top-down control of visual alpha-band oscillations (8-13 Hz), which have been consistently linked to mechanisms supporting the allocation of visuospatial attention. Given that items associated with contextual saliency (e.g., monetary reward or loss) attract attention, it is not surprising that the acquired salience of visual items further modulates. The executive networks controlling such reward-dependent modulations of oscillatory brain activity have yet to be fully elucidated. Although such networks have been explored in terms of corticocortical interactions, subcortical regions are likely to be involved. To uncover this, we combined MRI and MEG data from 17 male and 11 female participants, investigating whether derived measures of subcortical structural asymmetries predict interhemispheric modulation of alpha power during a spatial attention task. We show that volumetric hemispheric lateralization of globus pallidus (GP) and thalamus (Th) explains individual hemispheric biases in the ability to modulate posterior alpha power. Importantly, for the GP, this effect became stronger when the value saliency parings in the task increased. Our findings suggest that the GP and Th in humans are part of a subcortical executive control network, differentially involved in modulating posterior alpha activity in the presence of saliency. Further investigation aimed at uncovering the interaction between subcortical and neocortical attentional networks would provide useful insight in future studies.SIGNIFICANCE STATEMENT Whereas the involvement of subcortical regions into higher level cognitive processing, such as attention and reward attribution, has been already indicated in previous studies, little is known about its relationship with the functional oscillatory underpinnings of said processes. In particular, interhemispheric modulation of alpha band (8-13 Hz) oscillations, as recorded with magnetoencephalography, has been previously shown to vary as a function of salience (i.e., monetary reward/loss) in a spatial attention task. We here provide novel insights into the link between subcortical and cortical control of visual attention. Using the same reward-related spatial attention paradigm, we show that the volumetric lateralization of subcortical structures (specifically globus pallidus and thalamus) explains individual biases in the modulation of visual alpha activity.

Neural Circuit and Clinical Insights from Intraoperative Recordings During Deep Brain Stimulation Surgery

Observations using invasive neural recordings from patient populations undergoing neurosurgical interventions have led to critical breakthroughs in our understanding of human neural circuit function and malfunction. The opportunity to interact with patients during neurophysiological mapping allowed for early insights in functional localization to improve surgical outcomes, but has since expanded into exploring fundamental aspects of human cognition including reward processing, language, the storage and retrieval of memory, decision-making, as well as sensory and motor processing. The increasing use of chronic neuromodulation, via deep brain stimulation, for a spectrum of neurological and psychiatric conditions has in tandem led to increased opportunity for linking theories of cognitive processing and neural circuit function. Our purpose here is to motivate the neuroscience and neurosurgical community to capitalize on the opportunities that this next decade will bring. To this end, we will highlight recent studies that have successfully leveraged invasive recordings during deep brain stimulation surgery to advance our understanding of human cognition with an emphasis on reward processing, improving clinical outcomes, and informing advances in neuromodulatory interventions.

Modulations in Oscillatory Activity of Globus Pallidus Internus Neurons During a Directed Hand Movement Task-A Primary Mechanism for Motor Planning

Globus pallidus internus (GPi) neurons in the basal ganglia are traditionally thought to play a significant role in the promotion and suppression of movement via a change in firing rates. Here, we hypothesize that a primary mechanism of movement control by GPi neurons is through specific modulations in their oscillatory patterns. We analyzed neuronal spiking activity of 83 GPi neurons recorded from two healthy nonhuman primates executing a radial center-out motor task. We found that, in directionally tuned neurons, the power in the gamma band is significantly (p < 0.05) greater than that in the beta band (a "cross-over" effect), during the planning stages of movements in their preferred direction. This cross-over effect is not observed in the non-directionally tuned neurons. These data suggest that, during movement planning, information encoding by GPi neurons may be governed by a sudden emergence and suppression of oscillatory activities, rather than simply by a change in average firing rates.

Dysregulation of the Lateral Habenula in Major Depressive Disorder

Clinical and preclinical evidence implicates hyperexcitability of the lateral habenula (LHb) in the development of psychiatric disorders including major depressive disorder (MDD). This discrete epithalamic nucleus acts as a relay hub linking forebrain limbic structures with midbrain aminergic centers. Central to reward processing, learning and goal directed behavior, the LHb has emerged as a critical regulator of the behaviors that are impaired in depression. Stress-induced activation of the LHb produces depressive- and anxiety-like behaviors, anhedonia and aversion in preclinical studies. Moreover, deep brain stimulation of the LHb in humans has been shown to alleviate chronic unremitting depression in treatment resistant depression. The diverse neurochemical processes arising in the LHb that underscore the emergence and treatment of MDD are considered in this review, including recent optogenetic studies that probe the anatomical connections of the LHb.

Impulsivity in Parkinson's disease is associated with altered subthalamic but not globus pallidus internus activity

BACKGROUND

A significant subset of patients with Parkinson's disease (PD) suffer from impulse control disorders (ICDs). A hallmark feature of many ICDs is the pursuit of rewarding behaviours despite negative consequences. Recent evidence implicates the subthalamic nucleus (STN) and globus pallidus internus (GPi) in reward and punishment processing, and deep brain stimulation (DBS) of these structures has been associated with changes in ICD symptoms.

METHODS

We tested the hypothesis that in patients with PD diagnosed with ICD, neurons in the STN and GPi would be more responsive to reward-related stimuli and less responsive to loss-related stimuli. We studied a cohort of 43 patients with PD (12 with an ICD and 31 without) undergoing DBS electrode placement surgery. Patients performed a behavioural task in which their action choices were motivated by the potential for either a monetary reward or a monetary loss. During task performance, the activity of individual neurons was recorded in either the STN (n=100) or the GPi (n=100).

RESULTS

The presence of an ICD was associated with significantly greater proportions of reward responsive neurons (p<0.01) and significantly lower proportions of loss responsive neurons (p<0.05) in the STN, but not in the GPi.

CONCLUSIONS

These findings provide further evidence of STN involvement in impulsive behaviour in the PD population.

Subthalamic nucleus and globus pallidus interna influence firing of tonically active neurons in the primate striatum through different mechanisms

Both the subthalamic nucleus (STN) and the globus pallidus pars interna (GPi) are major targets for neuromodulation therapy for movement disorders. An example of such a therapy is deep brain stimulation (DBS). The striatum is the primary target for pharmacological treatment of these disorders. To further our understanding of both the functional relationships among motor nuclei and the mechanisms of therapies for movement disorders, it is important to clarify how changing the neuronal activity of one target, either by medication or by artificial electrical stimulation, affects the other connected nuclei. To investigate this point, we recorded single-unit activity from tonically active neurons (TANs), which are putative cholinergic interneurons in the striatum, of healthy monkeys (Macaca fuscata) during electrical stimulation of the STN or GPi. Both STN stimulation and GPi stimulation reduced the TAN spike rate. Local infusion of a D2 receptor antagonist in the striatum blocked the reduction in spike rate induced by STN stimulation but not that induced by GPi stimulation. Further, STN stimulation induced phasic dopamine release in the striatum as revealed by in vivo fast-scan cyclic voltammetry. These results suggest the presence of multiple, strong functional relationships among the STN, GPi, and striatum that have different pathways and imply distinct therapeutic mechanisms for STN- and GPi-DBS.

Seventy Years with the Globus Pallidus: Pallidal Surgery for Movement Disorders Between 1947 and 2017

The year 2017 marks the 70th anniversary of the birth of human stereotactic neurosurgery. The first procedure was a pallidotomy for Huntington's disease. However, it was for Parkinson's disease that pallidotomy was soon adopted worldwide. Pallidotomy was abandoned in the late 1950s in favor of thalamotomy because of the latter's more striking effect on tremor. The advent of levodopa put a halt to all surgery for PD. In the mid-1980s, Laitinen reintroduced the posteroventral pallidotomy of Leksell, and this procedure spread worldwide thanks to its efficacy on most parkinsonian symptoms including levodopa-induced dyskinesias and thanks to basic scientific work confirming the role of the globus pallidus internus in the pathophysiology of PD. With the advent of deep brain stimulation of the subthalamic nucleus, pallidotomy was again abandoned, and even DBS of the GPi has been overshadowed by STN DBS. The GPi reemerged in the late 1990s as a major stereotactic target for DBS in dystonia and, recently, in Tourette syndrome. Lately, lesioning of the GPI is being proposed to treat refractory status dystonicus or to treat DBS withdrawal syndrome in PD patients. Hence, the pallidum as a stereotactic target for either lesioning or DBS has been the phoenix of functional stereotactic neurosurgery, constantly abandoned and then rising again from its ashes. This review is a tribute to the pallidum on its 70th anniversary as a surgical target for movement disorders, analyzing its ebbs and flows and highlighting its merits, its versatility, and its resilience. © 2017 International Parkinson and Movement Disorder Society.

Anatomical brain difference of subthreshold depression in young and middle-aged individuals

BACKGROUND

Subthreshold depression (StD) is associated with substantial functional impairments due to depressive symptoms that do not fully meet the diagnosis of major depressive disorder (MDD). Its high incidence in the general population and debilitating symptoms has recently put it at the forefront of mood disorder research.

AIM

In this study we investigated common volumetric brain changes in both young and middle-aged StD patients.

METHODS

Two cohorts of StD patients, young and middle-aged, (n = 57) and matched controls (n = 76) underwent voxel-based morphometry (VBM).

RESULTS

VBM analysis found that: 1) compared with healthy controls, StD patients showed decreased gray matter volume (GMV) in the bilateral globus pallidus and precentral gyrus, as well as increased GMV in the left thalamus and right rostral anterior cingulate cortex/medial prefrontal cortex; 2) there is a significant association between Center for Epidemiological Studies Depression Scale scores and the bilateral globus pallidus (negative) and left thalamus (positive); 3) there is no interaction between age (young vs. middle-age) and group (StD vs. controls).

CONCLUSIONS

Our findings indicate significant VBM brain changes in both young and middle-aged individuals with StD. Individuals with StD, regardless of age, may share common neural characteristics.

The human subthalamic nucleus and globus pallidus internus differentially encode reward during action control

The subthalamic nucleus (STN) and globus pallidus internus (GPi) have recently been shown to encode reward, but few studies have been performed in humans. We investigated STN and GPi encoding of reward and loss (i.e., valence) in humans with Parkinson's disease. To test the hypothesis that STN and GPi neurons would change their firing rate in response to reward- and loss-related stimuli, we recorded the activity of individual neurons while participants performed a behavioral task. In the task, action choices were associated with potential rewarding, punitive, or neutral outcomes. We found that STN and GPi neurons encode valence-related information during action control, but the proportion of valence-responsive neurons was greater in the STN compared to the GPi. In the STN, reward-related stimuli mobilized a greater proportion of neurons than loss-related stimuli. We also found surprising limbic overlap with the sensorimotor regions in both the STN and GPi, and this overlap was greater than has been previously reported. These findings may help to explain alterations in limbic function that have been observed following deep brain stimulation therapy of the STN and GPi. Hum Brain Mapp 38:1952-1964, 2017. © 2017 Wiley Periodicals, Inc.